George Eliot once opined that adventure is not something outside man, but within. If so, the well of intrepidity within Sir Ranulph Fiennes – surely the world’s greatest living explorer – must be as bottomless as the pit of perdition.

This summer brings a chance to find out. For the rover has returned to talk publicly about his travels, triumphs and tussles with death. Taking in the relatively hospitable peaks of Guildford and Reading, Sir Ranulph’s theatre tour, Living Dangerously, tells the inspirational story of his record-breaking role in some of the most challenging expeditions of all time.

When I catch up with him, the fearless 70-year-old is in London, enduring a tedious round of sound checks ahead of the evening’s lecture. He seems aloof and restless of mind, as though eager to dispense with the pleasantries and begin scaling everything this side of sea level.

“It’s an authorial talk in which I’ll discuss selected expeditions and experiences,” he tells me, his voice clipped like that of a commanding officer.

“I’ll talk about what we did right, what went badly wrong and about competition with the Norwegians. I’ll talk about selecting people for expeditions and collecting millions from sponsors, and how we raised millions for charity.”

A modest sell. Yet Sir Ranulph’s story is unique and astounding. His exploits and escapades have taken him in almost every conceivable direction, embracing the first hovercraft expedition up the Nile in 1969 and the 52,000-mile odyssey that, from 1979-82, constituted the first polar circumnavigation of the Earth.

And that’s just the half of it. For Fiennes is also the first person to have made an unsupported crossing of Antarctica (1993), the first to cross that same continent on foot and the only man to have completed the arduous double of climbing Everest and crossing the polar ice caps.

His story, however, begins in more temperate climes and rather closer to home.

“I was born in the Princess Christian Nursing Home in Windsor,” he reveals. “At that time, in 1944, there were Doodlebugs falling everywhere.”

His initial stay in the Home Counties was short-lived, however, as personal tragedy triggered his first continental leap.

“My father was killed before I was born, leaving my mum with four children. My gran was 80 by this time, and she wanted to go back to South Africa where she was born. We had family out there and some cousins provided land. I go back regularly. I really do love the place.”

At age 12, the young Fiennes returned to these shores and attended Sandroyd School, Wiltshire, before going on to Eton. Academic success eluded him, however – even A levels proved beyond his grasp.

“In my defence, I failed largely because it was the height of the miniskirt era, which was something of a distraction,” he says wryly.

Then, in 1963, Ranulph joined the Royal Scots Greys of the British Army, from where he was later seconded to the SAS as a demolitions expert.

“I was very lucky to know from the very beginning exactly what I wanted to do with my life,” he reflects.

Fiennes, one senses, always speaks in these unwavering terms; as abrupt as a polar wind, as thick-skinned as his survival jacket.

“Many young men in their early-to-mid 20s have no idea,” he continues. “But I was brought up on stories of my father and uncle, who had fought and died in the world wars, and all I wanted was to do what they had done. I wanted to become a commanding officer.”

Ranulph’s appetite for adventure was further whetted by his three years spent fighting the Dhofar Rebellion, an increasingly radical uprising (1962-76) against the Sultanate of Muscat and Oman. For this he was decorated for bravery by the Sultanate.

“I enjoyed being there. I actually found myself increasingly identifying with the Muslims,” he says. “The Marxist rebels had a good base and had been trained in Odessa. They had a well-armed force of 4,500 against our 180.”

Was the transition from soldier to adventurer seamless?

“I came round to adventuring bit by bit. It was awkward leaving the army. And, of course, I had no money.”

What he did have, however, was the help of an equally intrepid adventurer, his late wife Virginia.

“Ginny was an incredible planner – just great,” he says, his tone one of comradely esteem more than anything. “In 1972 she planned the Transglobe Expedition on her six-inch school globe with a crayon.”

Another of Ran and Ginny’s accomplishments was the discovery of the lost city of Ubar, long buried in the sands of Oman and believed to be no more than a legend.

“That one took rather longer,” says Fiennes of the unlikely Arabian adventure. “But it received massive sponsorship. And Ginny was utterly determined to find the place.”

Ranulph’s death-defying endeavours are often perplexing. In 2003 he completed the first 7x7x7 Challenge – seven marathons, on seven continents, in seven consecutive days.

Unbelievably, this gruelling conquest came a mere three months after a massive heart attack, a three-day coma and a double bypass. Is he, I wonder, always this blasé about his health and wellbeing?

“Illness is certainly a nuisance, but in the end it’s unavoidable,” he says, casually. “You come to expect it once you pass the age of 45. It’s one of those things where all you can do is try to behave – not smoking, eating well and so on.”

Tragically, soon after Sir Ranulph’s uncannily rapid recovery, Ginny succumbed to bowel cancer and passed away in 2004. Yet the sad loss gave Fiennes renewed impetus in his support of charitable causes, and in 2007 he made what is arguably the world’s toughest ascent: the dreaded North Face of the Eiger. The feat raised £1.8m for Delivering Choice, the flagship programme of Marie Curie Cancer Care.

He also set his sights on what, in the end, proved an ill-fated attempt to climb Everest on the Tibetan side, hoping to raise £2m for the British Heart Foundation’s new research MRI scanner. He returned to the mountain in 2008 to climb the Nepalese side and raised a further £2.5m for Delivering Choice, this time coming within 400m of his elusive goal.

Finally, in 2009, Everest succumbed to his persuasive powers. At the slowly ripening age of 64, Sir Ranulph Fiennes became the oldest British man to reach the summit.

Few worlds remain to be conquered by this Alexander of the adventuring class. Today, says Sir Ranulph, the frontiers increasingly take the form of red tape.

“We’re held back by what the Foreign Office says we can and can’t do,” he grumbles. “So finding private backers who are free of such regulation is the ideal.”

Offers on a postcard, please. Preferably from somewhere truly remote.